Decking or shelving used in industrial and commercial storage racks has to be designed and constructed to bear heavy loads without twisting or buckling. For example, shelving used in bulk storage applications must be able to support the weight of densely packed rows of boxes filled with goods. In such applications, a solid steel sheet deck is a good choice for shelving because it has a high load-bearing capacity.
The design and construction of decking or shelving must comply, however, with the requirements of any fire codes applicable to the particular storage environment. Fire codes generally require that the surface area of each deck or shelf have a certain amount of open area, e.g., a number of holes distributed along the surface of the deck or shelf. A solid steel sheet deck would not meet this “open area” requirement and therefore could not be used as storage rack shelving or walkway decking.
The “open area” requirement serves two primary objectives from the standpoint of fire safety and prevention. First, the open area of each deck or shelf allows a fire that has broken out to move vertically up the storage rack instead of spreading horizontally to other storage racks, as the fire would do if it had broken out beneath a solid steel sheet deck. It also allows heat generated by the fire to dissipate instead of building up within a semi-enclosed space, as would be the case in a storage space between two solid steel sheet decks. In short, the open area creates a flue space within a storage rack, thereby causing the fire to travel upward and to release heat in the process. This maximizes the effectiveness of the sprinkler system in containing the fire because it allows the fire to reach the sprinkler heads as quickly as possible without building up too much heat and intensity.
Second, the open area of each deck or shelf allows water from an overhead sprinkler system to flow downward in the event of a fire. As long as water runs freely through the individual decks or shelves, an overhead sprinkler system can adequately contain a fire breaking out at any shelving level and prevent it from spreading to other storage racks.
The amount of open area generally required by fire codes is fifty percent (50%) of the surface area. Lower percentages may be allowed, however, depending on the particular storage environment. As pointed out above, a solid steel sheet deck does not have any open area and therefore would not meet this “fifty-percent” rule. Consequently, it could not be used in bulk storage applications even though it has a high load-bearing capacity.